Group III nitride semiconductor crystals such as GaN are widely used to form optical devices such as light-emitting diode and laser, or high-frequency devices such as diode and transistor, and are expected to be used for power devices in the future.
Since many of these devices are obtained by epitaxial growth on a GaN substrate using the metal-organic vapor phase epitaxy (MOVPE) method, etc., characteristics of GaN substrate have a great impact even on device characteristics. Therefore, many studies to obtain high-quality GaN substrates have been actively conducted.
A method for manufacturing high-quality GaN substrate has been proposed, in which a GaN base substrate is formed by a liquid phase growth method such as the Na flux method and a thick GaN crystal is further grown thereon by the hydride vapor phase epitaxy (HYPE) method (see, e.g., PTLs 1 and 2).
In this method, since the liquid phase growth method characterized in less crystal defect occurrence and small variation in crystal orientation distribution due to warpage of crystal but low crystal growth rate is combined with the HYPE method characterized in more probability of defect occurrence but the high crystal growth rate, the two methods make up the respective shortcomings. Specific processes are disclosed in PTLs 1 and 2, etc.
Meanwhile, one of the methods capable of efficiently manufacturing a large high-quality Group III-V compound crystal with only few defects is a method for manufacturing a Group III-V compound crystal including a seed crystal-forming substrate providing step for providing a seed crystal-forming substrate (so-called point-seed substrate) having plural Group III-V compound seed crystals on a substrate, a contact step for bringing metal melt into contact with the surfaces of the plural Group III-V compound seed crystals, and a crystal growth step for forming and growing Group III-V compound crystals using the Group III-V compound seed crystals as nuclei by reacting a group III element with Group V element in the metal melt, wherein the plural Group III-V compound crystals grown from the plural Group III-V compound seed crystals are connected as their growth progresses in the crystal growth step, and a Group III-V compound layer formed on the substrate is partially removed by a physical process to form the plural Group III-V compound seed crystals (see PTL 3). Non-patent literatures 1 and 2 also disclose similar related techniques.